Add session & user management in the backend

app/controllers/application_controller.rb

@@ -1,4 +1,14 @@
 class ApplicationController < ActionController::Base
   # Only allow modern browsers supporting webp images, web push, badges, import maps, CSS nesting, and CSS :has.
   allow_browser versions: :modern
+
+  def logged_in?
+    if session[:user_id] then true else false end
+  end
+
+  def current_user
+    if logged_in?
+      session[:user_id]
+    end
+  end
 end